Book IV chapter 13

The observations of variation by seamen¹ vary, for the most part, and are uncertain: partly from error and inexperience, and the imperfections of the instruments; and partly from the sea being seldom so calm that the shadows or lights can remain quite steady on the instruments.

A fter the variation of the compass had first been noticed, some more diligent² navigators took pains to investigate in various ways the difference of aspect of the mariners³' compass. Yet, to the great detriment⁴ of the nautical⁵ art, this has not been done so exactly as it ought to have been. For either being somewhat ignorant they have not understood any accurate method or they have used bad and absurd instruments, or else they merely follow some conjecture⁶ arising from an ill-formed opinion as to some prime meridian⁷ or magnetick pole; whilst others again transcribe⁸ from others, and parade these observations as their own; and they who, very unskilful themselves, first of all committed their observations to writing are, as by the prerogative¹⁰ of time, held in esteem¹¹ by others, and their posterity¹² does not think it safe to differ from them. Hence in long navigations, especially to the East Indies, the records by the Portuguese¹³ of the deviating¹⁴ compass are seen to be unskilful: for whoever reads their writings will easily understand that they are in error in very many things, and do not rightly understand the construction of the Portuguese compass (the lily of which diverges¹⁵ by half a rumbe from the needles toward the west), nor its use in taking the variation. Hence, while they show the variation of the compass in different places, it is uncertain whether they measure the deviation¹⁶ by a true meridional compass or by some other whose needles are displaced from the lily. The Portuguese (as is patent in their writings) make use of the Portuguese compass, whose magnetick needles are fixed¹⁷ aside from the lily by half of one rumbe toward the east. Moreover on the sea the observation of the variation is a matter of great difficulty, on account of the motion of the ship and the uncertainty¹⁸ of the deviation, even with the more skilful⁹ observers, if they use the best made instruments hitherto known and used. Hence there arise different opinions concerning the magnetick deviation: as, for instance, near the Island of St. Helena the Portuguese Rodriguez de Lagos measures half a rumbe. The Dutch in their nautical log fix it at a whole rumbe. Kendall, the expert Englishman, with a true meridional compass admits only a sixth part of a rumbe. A little to the East of Cape¹⁹ Agullias Diego Alfonso makes no variation, and shows by an Astrolabe that the compass remains²⁰ in the true meridian. Rodriguez shows that the compass at Cape Agulhas has no variation if it is of Portuguese construction, in which the needles are inclined half a rumbe to the East. And there is the same confusion, negligence²¹, and vanity in very many other instances.

1 seamen   

n.海员

参考例句：

• Experienced seamen will advise you about sailing in this weather. 有经验的海员会告诉你在这种天气下的航行情况。
• In the storm, many seamen wished they were on shore. 在暴风雨中，许多海员想，要是他们在陆地上就好了。

2 diligent   

adj.勤勉的，勤奋的

参考例句：

• He is the more diligent of the two boys.他是这两个男孩中较用功的一个。
• She is diligent and keeps herself busy all the time.她真勤快，一会儿也不闲着。

3 mariners   

海员，水手（mariner的复数形式）

参考例句：

• Mariners were also able to fix their latitude by using an instrument called astrolabe. 海员们还可使用星盘这种仪器确定纬度。
• The ancient mariners traversed the sea. 古代的海员漂洋过海。

4 detriment   

n.损害；损害物，造成损害的根源

参考例句：

• Smoking is a detriment to one's health.吸烟危害健康。
• His lack of education is a serious detriment to his career.他的未受教育对他的事业是一种严重的妨碍。

5 nautical   

adj.海上的，航海的，船员的

参考例句：

• A nautical mile is 1,852 meters.一海里等于1852米。
• It is 206 nautical miles from our present location.距离我们现在的位置有206海里。

6 conjecture   

n./v.推测，猜测

参考例句：

• She felt it no use to conjecture his motives.她觉得猜想他的动机是没有用的。
• This conjecture is not supported by any real evidence.这种推测未被任何确切的证据所证实。

7 meridian   

adj.子午线的；全盛期的

参考例句：

• All places on the same meridian have the same longitude.在同一子午线上的地方都有相同的经度。
• He is now at the meridian of his intellectual power.他现在正值智力全盛期。

8 transcribe   

v.抄写，誉写；改编(乐曲)；复制，转录

参考例句：

• We need volunteers to transcribe this manuscript.我们需要自愿者来抄写这个文稿。
• I am able to take dictation in English and transcribe them rapidly into Chinese.我会英文记录，还能立即将其改写成中文。

9 skilful   

(=skillful)adj.灵巧的，熟练的

参考例句：

• The more you practise,the more skilful you'll become.练习的次数越多，熟练的程度越高。
• He's not very skilful with his chopsticks.他用筷子不大熟练。

10 prerogative   

n.特权

参考例句：

• It is within his prerogative to do so.他是有权这样做的。
• Making such decisions is not the sole prerogative of managers.作这类决定并不是管理者的专有特权。

11 esteem   

n.尊敬，尊重；vt.尊重，敬重；把…看作

参考例句：

• I did not esteem him to be worthy of trust.我认为他不值得信赖。
• The veteran worker ranks high in public love and esteem.那位老工人深受大伙的爱戴。

12 posterity   

n.后裔，子孙，后代

参考例句：

• Few of his works will go down to posterity.他的作品没有几件会流传到后世。
• The names of those who died are recorded for posterity on a tablet at the back of the church.死者姓名都刻在教堂后面的一块石匾上以便后人铭记。

13 Portuguese   

n.葡萄牙人；葡萄牙语

参考例句：

• They styled their house in the Portuguese manner.他们仿照葡萄牙的风格设计自己的房子。
• Her family is Portuguese in origin.她的家族是葡萄牙血统。

14 deviating   

v.偏离，越轨( deviate的现在分词 )

参考例句：

• I compromise by using a prepared text and deviating from it whenever I feel the need. 我搞折衷办法，准备一份讲稿，觉得需要的时候就自由发挥。 来自辞典例句
• Theories deviating practices are inane, while practices deviating theories are blindfold. 脱离实践的理论是空泛的，脱离理论指导的实践是盲目的。 来自互联网

15 diverges   

分开( diverge的第三人称单数 )； 偏离； 分歧； 分道扬镳

参考例句：

• The beam of flashlight diverges, but it can be refocused with lenses. 一个发散的闪光灯束可以用透镜重新聚焦。
• At the end of the wood, the path diverges to the left. 在树林的尽头，小路向左拐去。

16 deviation   

n.背离，偏离；偏差，偏向；离题

参考例句：

• Deviation from this rule are very rare.很少有违反这条规则的。
• Any deviation from the party's faith is seen as betrayal.任何对党的信仰的偏离被视作背叛。

17 fixed   

adj.固定的，不变的，准备好的；(计算机)固定的

参考例句：

• Have you two fixed on a date for the wedding yet?你们俩选定婚期了吗？
• Once the aim is fixed,we should not change it arbitrarily.目标一旦确定，我们就不应该随意改变。

18 uncertainty   

n.易变，靠不住，不确知，不确定的事物

参考例句：

• Her comments will add to the uncertainty of the situation.她的批评将会使局势更加不稳定。
• After six weeks of uncertainty,the strain was beginning to take its toll.6个星期的忐忑不安后，压力开始产生影响了。

19 cape   

n.海角，岬；披肩，短披风

参考例句：

• I long for a trip to the Cape of Good Hope.我渴望到好望角去旅行。
• She was wearing a cape over her dress.她在外套上披着一件披肩。

20 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

21 negligence   

n.疏忽，玩忽，粗心大意

参考例句：

• They charged him with negligence of duty.他们指责他玩忽职守。
• The traffic accident was allegedly due to negligence.这次车祸据说是由于疏忽造成的。